txorphanage: Extract GetOrphanTx

Extract orphan lookup code into GetOrphanTx function.

src/txorphanage.cpp

@@ -129,3 +129,11 @@ bool HaveOrphanTx(const GenTxid& gtxid)
     }
 }
 
+std::pair<CTransactionRef, NodeId> GetOrphanTx(const uint256& txid)
+{
+    AssertLockHeld(g_cs_orphans);
+
+    const auto it = mapOrphanTransactions.find(txid);
+    if (it == mapOrphanTransactions.end()) return {nullptr, -1};
+    return {it->second.tx, it->second.fromPeer};
+}